Engine/Transmission (1994 - 1998) Major EGT issues

[LVJUNIOR]

Any updates LV?

Been keeping my fingers crossed that you found the culprit.

That is a tough question to answer due to the fact the temperature dropped 30° here which will have a big effect on egt. That being said here is the update:

I put in the new injectors which are 5x11 sac nozzles with 145° spray angle. I also think I figured out the flat spot issue. The way the AFC was set up the pre-boost fueling screw was turned in about 1/4" putting a preload on the AFC foot. The preload caused the foot to not move until 12 psi of boost with max travel only being at 25psi. The pre-boost fuel was enough to get it to 10psi quickly then it would flatten out until it gradually got to 12 psi and started moving the foot which would then fuel very hard very quickly.

I backed the pre- boost fuel screw all the way down and slid the AFC housing full forward. While the AFC was off I also did the washer mod and the foot mod to gain travel. The Foot will now move with 2-4psi and doesn't max out until 35psi. When I put the AFC housing back on it was light on pre-boost fuel so I have been working to tune that. Every time I drive it I get out and give the pre-boost fuel screw 1/8 of a turn. I will continue this until that section is perfect. Then I will start working on the star wheel adjustment in the same manner.

Not being fully tuned at this point I don't know how the EGTs will end up but as of right now I am seeing some of the coolest EGTs I have ever had cruising at highway speeds and my boost at 75mph has dropped by 10psi. The motor seems much smoother than it has ever been. I am working a ton and don't have the time to tow with it as I drive a work truck all week but as soon as I take it on a good long pull I will update my post.

 

[JesseGray]

I have been following this thread closely, since I am having the same issues with my 97. My 12Vis equipped with 3. 51 rear end, 5spd Manual, 62x12 HTT Quick Spool (HX35) Turbo, 4" exhaust turbo back, BD 5 fuel plate, BHAC pulling air from fender and engine compartment. The radiator has been recently flushed, a two year old water pump and thermostat, new stage II injectors, no waste gate, and the CAC is clear.



This setup worked great on an 8,000 mile trip (with the fifth wheel) San Diego to Providence, RI. On the return trip, it began to smoke on acceleration and go away. The black smoke became more frequent, progressing to the black smoke cloud on acceleration.



Returning home yesterday with my 11,000 lb fifth wheel along the continental Divide, from the injection shop, I could almost instantly go to 1300 degrees on the EGTs and 30 psi in boost. The engine has plenty of power and acceleration---except for the EGTs and dark black smoke. The engine temp stayed with in 190 to 200 degree range. I was able to pull the several grades at 60 mph in 4th gear pulling 25" of boost and keeping the EGTs under 1200 degrees.



We changed the injectors, thinking that one was pouring raw fuel into the cylinders causing the black smoke and high EGTs. The new injectors increased the power and acceleration significantly, but did not reduce the smoke.



I am wondering about a bad valve, or a bad valve spring. Would the star wheel have any affect?



LVJunior and I are struggling with the same or similar issues.



I appreciate everyone's comments, since it helps with my check list.